GUCA2B and irritable bowel syndrome: Using the same study cohort, the aims of this study were to determine whether there is abnormality in the density of uroguanylin immunoreactive cells in the duodenum of IBS patients compared to healthy controls (controls), to study the effect of changing the gut microbiota through FMT on the density of these cells, and to find the correlations between these cells and IBS symptoms (if any).